Update usage in README

[rbdr/serpentity] / lib / serpentity.js

// Export submodules
export { Component } from './serpentity/component.js';
export { Entity } from './serpentity/entity.js';
export { Node } from './serpentity/node.js';
export { System } from './serpentity/system.js';

import { NodeCollection } from './serpentity/node_collection.js';

/*
Serpentity is a simple entity framework inspired by Ash.

Usage:

    import Serpentity from '@serpentity/serpentity';

## Instantiating an engine

    const engine = new Serpentity();

Add entities or systems, systems are added with a priority (the smaller
the number, the earlier it will be called):

    engine.addEntity(entityFactory());
    engine.addSystem(new GameSystem(), priority);

Update all systems:

    engine.update(dt);

Remove entities or systems:

    engine.removeEntity(entityReference);
    engine.removeSystem(systemReference);

## Creating Entities

Entities are the basic object of Serpentity, and they do nothing.

    import { Entity } from '@serpentity/serpentity';
    const entity = new Entity();

All the behavior is added through components

## Creating Components

Components define data that we can add to an entity. This data will
eventually be consumed by "Systems"

    import { Component } from '@serpentity/serpentity';
    const PositionComponent = class PositionComponent extends Component {
      constructor(config) {

        this.x = 0;
        this.y = 0;

        super(config);
      }
    };

You can add components to entities by using the add method:

    entity.addComponent(new PositionComponent());


Systems can refer to entities by requesting nodes.

## Working with Nodes

Nodes are sets of components that you define, so your system can require
entities that always follow the API defined in the node.

    import { Node } from '@serpentity/serpentity';
    const MovementNode = class MovementNode extends Node;
    MovementNode.position = PositionComponent;
    MovementNode.motion = MotionComponent;

You can then request an array of all the nodes representing entities
that comply with that API

    engine.getNodes(MovementNode);

## Creating Systems

Systems are called on every update, and they use components through nodes.

    import { System } from '@serpentity/serpentity';
    const TestSystem = class TestSystem extends System {
      added(engine){

        this.nodeList = engine.getNodes(MovementNode);
      }

      removed(engine){

        this.nodeList = undefined;
      }

      update(dt){

        for (const node of this.nodeList) {
          console.log(`Current position is: ${node.position.x},${node.position.y}`);
        }
      }
    };

## That's it

Just run `engine.update(dt)` in your game loop :D

*/
export default class Serpentity {

  constructor(config) {

    this.systems = [];
    this.entities = [];
    this._nodeCollections = [];
    this._nodeCollectionKeys = [];

    Object.assign(this, config);
  }

  /*
   * Adds a system to the engine, so its update method will be called
   * with the others. Triggers added hook.
   *
   * returns true if added succesfully, false if already added
   */
  addSystem(system, priority) {

    if (this.systems.indexOf(system) >= 0) {
      return false;
    }

    system.priority = priority;

    let lastIndex = 0;

    const found = this.systems.some((existingSystem, i) => {

      lastIndex = i;
      if (existingSystem.priority >= system.priority) {
        return true;
      }
    });

    if (!found) {
      lastIndex += 1;
    }

    this.systems.splice(lastIndex, 0, system);
    system.added(this);
    return true;
  }

  /*
   * Removes a system from the engine, so its update method will no
   * longer will be called. Triggers the removed hook.
   *
   * returns true if removed succesfully, false if already added
   */
  removeSystem(system) {

    const position = this.systems.indexOf(system);
    if (position >= 0) {
      this.systems[position].removed(this);
      this.systems.splice(position, 1);
      return true;
    }

    return false;
  }

  /*
   * Adds an entity to the engine, adds to existing node collections
   *
   * returns true if added, false if already there
   */
  addEntity(entity) {

    if (this.entities.indexOf(entity) >= 0) {
      return false;
    }

    this.entities.push(entity);

    for (const collection of this._nodeCollections) {
      collection.add(entity);
    }

    return true;
  }

  /*
   * Removes entity from system, removing from all node collections
   *
   * returns true if removed, false if not present
   */
  removeEntity(entity) {

    const position = this.entities.indexOf(entity);
    if (position >= 0) {
      for (const collection of this._nodeCollections) {
        collection.remove(entity);
      }

      this.entities.splice(position, 1);
      return true;
    }

    return false;
  }

  /*
   * Given a Node Class, retrieves a list of all the nodes for each
   * applicable entity.
   */
  getNodes(nodeType) {

    const position = this._nodeCollectionKeys.indexOf(nodeType);

    if (position >= 0) {
      return this._nodeCollections[position].nodes;
    }

    const nodeCollection = new NodeCollection({
      type: nodeType
    });

    this._nodeCollectionKeys.push(nodeType);
    this._nodeCollections.push(nodeCollection);

    for (const entity of this.entities) {
      nodeCollection.add(entity);
    }

    return nodeCollection;
  }

  /*
   * Calls update for every loaded system.
   */
  update(dt) {

    for (const system of this.systems) {
      system.update(dt);
    }
  }
}